Evaluation methods for projection images captured by means of x-ray systems are generally known.
An evaluation method for projection images is known from the technical article “Quantitative Analyse von Koronarangio-graphisichen Bildfolgen zur Bestimmung der Myokardperfusion”[Quantitative analysis of coronary angiographic image sequences for determining the myocardial perfusion] by Urban Malsch et al., published in “Bildverarbeitung für die Medizin 2003”, Bildverarbeitung für die Medizin 2003—Algorithmen—Systeme—Anwendungen,[Image processing for medical science 2003—algorithms, systems, applications], Springer-Verlag, pages 81-85. With this evaluation method, a computer uses the projection images to determine a 2-dimensional evaluation image that has a plurality of pixels and outputs the evaluation image to a user by mean of a monitor. The pixels of the evaluation image correspond to those of the projection images. The computer uses the time characteristic of the pixel values of the projection images to assign a pixel value to the pixels of the evaluation image. The pixel value of the evaluation image is characteristic of the time point of the maximum contrast change.
A similar disclosure is given in the technical article “Estimating Perfusion Using x-ray Angiography” by Hrvoje Bogunovic and Sven Loncaric. This technical article is published in the Proceedings of the 4th International Symposium on Image and Signal Processing and Analysis (2005), pages 147 to 150. According to this technical article, a subtraction of a reference image from the projection images takes place.
The doctrines of the two latter-named technical articles are described in the context of angiographic examinations of coronary vessels of the human heart. This type of examination is at present one of the most important diagnostic aids of cardiology. Additional information such as the determination of the rate of flow or the myocardial perfusion is further information that can be obtained by means of angiography. The essential diagnostic evidence is the perfusion of the myocardium.
The quantification of the blood flow through the myocardium using an angiographic procedure is problematic because the coronary vessels when angiographically observed have a diameter of barely 1 mm or more. These observed vessels end in millions of tiny capillary vessels which have diameters of only a few micrometers. The flow dynamics and distribution in the capillary vessels finally determines the blood supply of the myocardium. Inference of the macroscopic blood flow of the observed coronary vessels on the dynamics and distribution of the blood flow in the capillary vessels is strictly speaking not permissible but such conclusions are, however, often drawn on this basis.
Angiographic-based heart perfusion imaging carries out long recordings, with the recordings lasting until the contrast medium has passed through the coronary vessels and is visible in the myocardium itself. This latter phase is known as “myocardial blush”. The “myocardial blush” is assessed to obtain evidence of the supply of the heart with blood and, for example, to gauge the success of therapies and/or estimate the risk profile for the patient.
To make the blood flow dynamics in large vessels and in the capillary vessels measurable and therefore comparable, various gradation systems are known that divide the continuum of the possible conditions into discrete classes. Many of these classifications describe the macroscopic blood circulation and others the capillary blood circulation. The most common classifications were determined by the scientific organization “Thrombolysis in Myocardial Infarction” (TIMI). These classifications are regarded as standard. The TIMI classifications are frequently used in multicentric studies where it is particularly a question of reproducible and comparable results. These classifications are, however, complex and can be used only by expending considerable time. They are not usually used in routine clinical work.
By far the most frequently used method according to prior art is the visual estimation of the myocardial blush on the monitor. This procedure is often used for multicentric studies. A precondition for this procedure is that the angiographic recording is sufficiently long to enable the introduction and washout of the contrast medium to be detected. The visual estimation requires much experience and in practice is carried out only by TIMI-blush experts.
Procedures are also known by means of which a computer-aided attempt is made at a visual subjective-personal estimation. An example of such a method is given in the aforementioned technical articles by Urban Maltsch and Bogunovic.
Although the procedures in the aforementioned technical articles represent a good starting point they still have shortcomings. In particular, it is necessary with the procedures according to the technical articles to identify the vessels of the vascular system in the projection images in order to be able to hide these vessels when evaluating the myocardial blush. It is also necessary with the procedures according to the technical articles to operate with DSA images. This presents a distinct danger of artifacts. Computer intensive processors for movement compensation are necessary to avoid artifacts.
Evaluation methods for 2-dimensional projection images are also described in German patent application DE 10 2005 039 189.3. This patent application was still not available to the public on the date of filing of this present invention and does not represent a general prior art. This patent application has to be examined with regard to novelty only in the German patent granting procedure. The method described in patent application DE 10 2005 039 189.3 is already very effective. In particular, an automatic identification of the vessels of the vascular system is possible by means of this method. Furthermore with the evaluation method described therein it is not absolutely necessary to work with DSA images.